TEPCO Fukushima Daini Nuclear Power Station Research on the status of response to the Tohoku-Pacific Ocean

TEPCO Fukushima Daini Nuclear Power Station Research on the status of response to the Tohoku-Pacific Ocean

TEPCO Fukushima Daini Nuclear Power Station Research on the status of response to the Tohoku-Pacific Ocean

TEPCO Fukushima Daini Nuclear Power Station Research on the status of response to the Tohoku-Pacific Ocean Earthquake and Tsunami and Lessons learned therefrom (Proposals) October 2012 Japan Nuclear Safety Institute

TEPCO Fukushima Daini Nuclear Power Station Research on the status of response to the Tohoku-Pacific Ocean

Table of contents 1. Introduction . . 2 2. Overview of Fukushima Daini Nuclear Power Station . . 4 2.1 Overall Layout . . 4 2.2 System Configuration . . 5 2.3 Power Supply System . . 7 2.4 Severe Accident Countermeasures; Accident Management . . 9 3. Overview of the tsunami caused by the Tohoku-Pacific Ocean Earthquake . . 11 3.1 Overview of the Earthquake and the tsunami .

. 11 3.2 Results of observation at Fukushima Daini . . 15 3.3 Data on the earthquake and subsequent tsunami . . 16 3.4 Damage of Equipment . . 17 3.4.1 Damage by the earthquake . . 17 3.4.2 Damage by the tsunami . . 19 4. Response to the accident at Fukushima Daini . . 23 4.1 Response status from the time of the earthquake and tsunami until restoration and cold shutdown . . 29 4.2 Emergency response situation . . 30 4.2.1 Immediately after the earthquake . . 30 4.2.2 Immediately after the arrival of the tsunami . . 33 4.2.3 Responses toward restoration after the arrival of the tsunami . . 34 4.2.3.1 Overview of the power plant .

. 34 4.2.3.2 Situation of Fukushima Daini Unit 1 . . 38 4.2.3.3 Situation of Fukushima Daini Unit 2 . . 39 4.2.3.4 Situation of Fukushima Daini Unit 3 . . 41 4.2.3.5 Situation of Fukushima Daini Unit 4 . . 42 4.3 Cooling of spent fuel pool of Fukushima Daini . . 44 5. Analysis of accident response . . 45 5.1 Purpose of the analysis of accident response . . 45 5.2 Concept of analysis . . 45 5.3 Specific analysis procedures . . 46 5.4 Important lessons obtained from the analysis . . 59 6. Emergency response as seen from the viewpoint of the human factor . . 61 7. Lessons . . 64 7.1 Organization, management, communication .

. 64 7.2 Advance preparation (equipment, manual, training . . 65 7.3 Initial response in the accident . . 66 7.4 Additional measures . . 67 8. Conclusion . . 68 Attachment Recommended Actions for the Emergency Response by Equipments/Materials Reinforcement . . 69

TEPCO Fukushima Daini Nuclear Power Station Research on the status of response to the Tohoku-Pacific Ocean

1. Introduction. For everyone associated with nuclear power, March 11, 2011 has become a day which will never be forgotten. This day will be long remembered by those in the nuclear industry for years to come. Even now, a large number of people still have to endure stressful lives as refugees. If we consider the length of time as well as the size and range of the damage, we will profoundly recognize the enormity of the damage of the nuclear disaster. Meanwhile, TEPCO’s Fukushima Daiichi Nuclear Power Station (hereinafter referred to as "Fukushima Daiichi"), is in the middle of a restoration process for accident convergence in accordance with the roadmap, and the situation of the power plant may be considered to have subsided substantially.

National agencies, local governments, industries, academia, volunteer groups and local residents are making efforts for decontamination and other tasks toward the restoration of the region, and as a result, some areas have managed to relax access restriction. Although there were the most stringent controls on the shipment of food from the outset of the accident, restrictions have been lessened little by little but it is still necessary to continue the constant monitoring. The level of radiation to which residents are exposed is regulated based on knowledge of the dose rate obtained from historical data, including survivors of the atomic bombs dropped on Hiroshima and Nagasaki, but this is not considered to provide clarity in indicating the late-onset effects of radiation exposure, and we do not think that a situation will develop in which there will be significant increase in cancer incidence due to radioactive materials.

The national government will continuously monitor the health of residents in the future. Extensive validations have been performed about the Fukushima Daiichi accident, and many reports have been published. Our Institute has also issued a proposal with the cooperation of TEPCO and manufacturers which was published at the end of last October as a statement from the industry. It focuses primarily on the hardware to combat tsunami to prevent accidents from expanding. We believe that the expansion of this accident and the massive release of radioactive materials into the environment could have been prevented if appropriate measures had been taken.

Dr. Hatamura, Chairman of the Accident Investigation Committee of the government, stated in a special NHK program that "this accident at Fukushima Daiichi could have been averted if proper and adequate preparations had been in place.” There is an ongoing national discussion of what to do about the energy supply in the future; we think that inexpensive natural energy is not sufficient at present, and will not be secure in the future, and that considering big problems such as energy security, global warming, and remaining internationally competitive (the hollowing out of domestic industry), it would be unrealistic to eliminate all nuclear power entirely.

Before the accident at Fukushima Daiichi, the Democratic Party, the current ruling party, promised the international community a 25% reduction of CO2 emissions and was planning to increase the proportion of nuclear power to 40%. How we can achieve our international commitment to CO2 reduction without nuclear power? And how long we can continue to pay as much as three trillion yen each year to operate thermal power plants instead of nuclear power plants, in addition to buying fossil fuels? In view of these difficult issues, we think that the realistic option for the time being is to continue using nuclear power while improving its safety.

Following the industry report analyzing the Fukushima Daiichi accident, our Institute decided 2

to validate the post-tsunami response situation at the Fukushima Daini Nuclear Power Station (hereinafter referred to as "Fukushima Daini") which successfully led the station to convergence, both from a technical perspective and from the viewpoint of a third party, with the intent of gathering lessons in order to enhance the accident response capability of nuclear power plants and contribute to the improvement of safety. Details of the sequence of events and responses to the Fukushima Daini accident have already been fully described in the accident analysis reports such as by the Government and by TEPCO.

Therefore, this report is dedicated to summarizing the overview of the sequence of events and accident responses, and it is intended to pick out good practices which include lessons for the future. In compiling these lessons, we tried to make our recommendations as specific as possible by describing the necessary level of preparedness based on the actual accident responses.

We hope that the lessons of this report will be utilized when nuclear power plants in Japan and throughout the world consider possible measures against accidents. As stated above, our report on the Fukushima Daiichi accident, which primarily summarizes the hardware and recommends various measures, is available at the Japan Nuclear Safety Institute’s website (former Japan Nuclear Technology Institute). Please visit the page. In this report, we basically excluded the analysis of the activities of the central and local governments and confined our analysis to gathering lessons about aspects to which electric utility companies should be able to respond.

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2. Overview of Fukushima Daini Nuclear Power Station 2.1 Overall Layout Fukushima Daini is located in the towns of Naraha and Tomioka in Futaba-gun, Fukushima Prefecture, about 12 km south of Fukushima Daiichi, facing the Pacific Ocean to the east. The site is approximately 147 million m2 and its shape is almost square. At present, four units of boiling water reactors have been installed and are arranged in the order of No. 1, 2, 3, and 4 from the south. The generating capacity of these units is 1,100 MW each, making for a total installed capacity of power generation of 4,400 MW.

When the recent disaster occurred, all units 1 to 4 were in operation at the rated thermal output.

One central control room controls two units of reactors in a twin plant design: Units 1 and 2 make up one pair and Units 3 and 4 another. Type Location Unit Start of Operation Reactor Pressure Vessel Output(MW) Situation when event happened 1 S57.4 Mark II 1,100 Naraha town 2 S59.2 1,100 3 S60.6 1,100 Tomioka town 4 S62.8 BWR5 Mark II R Advanced 1,100 In operation at the rated thermal output Fig 2.1 Overall Layout of Power Stations Waste Treatment Building Unit 4 Unit 3 Unit 2 Unit 1 Main Office Building Important Seismic Isolation Building Reactor Building Turbine Building Seawater Heat Exchanger Building 4

2.2 System Configuration The system configuration of each unit of Fukushima Daini is as shown in Fig 2.2. The role of each system is as follows: • Reactor Core Isolation Cooling System (RCIC) In the event that the main condenser is no longer available for any reason, such as closure of the main steam isolation valve during normal operation, steam from the reactor will activate the turbine drive pump to inject the water in the condensate storage tank (referred to as "CST" below) into the reactor, and reduce the pressure by removing the decay heat of the fuel. The system also works as an emergency water injection pump in case of the failure of the water supply system, etc., and maintains the water level in the reactor.

• Residual Heat Removal System (RHR) After shutting down the reactor, the system will cool the coolant (remove the decay heat of the fuel) using pumps and the heat exchangers, or maintain the level of reactor water by injecting cooling water in case of an emergency (part of ECCS). The system has the ability to bring the reactor to cold shutdown and has five modes of operation: reactor shutdown cooling mode, low-pressure injection mode (ECCS), containment spray mode, pressure suppression chamber cooling mode, and emergency heat load mode. • Emergency Core Cooling System (ECCS) The system consists of four subsystems: low pressure core spray system (LPCS), low pressure water injection system, high pressure core spray system (HPCS) and automatic depressurization system.

In the case that a loss-of-coolant accident (LOCA) has occurred due to a piping break in the reactor coolant pressure boundary, such as the primary loop recirculation system piping, the system will remove the residual heat and the decay heat of the fuel in the reactor core, preventing the fuel cladding tube from being damaged by the fuel overheating, and consequently, minimize and suppress the water-zirconium reaction to a negligible extent.

• Standby Liquid Control System (SLC) If and when control rod insertion becomes impossible for any reason during reactor operation, the system will inject a neutron-absorbing boric acid solution from the bottom of the reactor core as a backup for the control rod to stop the nuclear reaction. 5

Fig 2.2-1 System configuration of Fukushima Daini Unit 1 and 2 Fig 2.2-2 System configuration of Fukushima Daini Unit 3 and 4 RCIC Pump Water Pump (Turbine driven, 2 units) CST, from Suppression Pool Water Pump (Motor driven, 2 units) to Suppression Pool Condensate Pump (High Pressure, 3 units) (Low Pressure, 3 units) Main Turbine Condenser Circulating Water Pump (3 units) Sea Condensate Storage Tank (CST) to RHR MUWC Pump *2 to HPCS RCIC CRD *1 PLR (A) in Unit1, PLR (B) in Unit 2 *2 Pump three units in Unit 1, two units in Unit 2 from MUWC Pump to RHR (B) Pump HPCS Pump RHR (A) Pump to RCIC CRD Pump, 2 units from CST from CST SLC Tank SLC Pump, 2 units LPCS Pump from PLR (A) RHR (B) Pump RHR (C) Pump to Suppression Pool RCIC Pump Water Pump (Turbine driven, 2 units) Water Pump (Motor driven, 2 units) Condensate Pump (3 units) Main Turbine Condenser Circulating Water Pump (3 units) Sea Condensate Storage Tank (CST) to RHR MUWC Pump (3 units) to HPCS RCIC CRD from MUWC Pump to RHR (B) Pump HPCS Pump RHR (A) Pump to RCIC CRD Pump, 2 units from CST from CST SLC Tank SLC Pump, 2 units LPCS Pump from PLR (B) RHR (B) Pump RHR (C) Pump CST, from CST, S/P 6

2.3 Power Supply System The electricity generated by these units is transmitted via two 500 kV lines (Tomioka Line) to the power grid. The transmission capacity of one Tomioka line is sufficient for all the electricity generated at Fukushima Daini, and therefore the power plant can continue full output generation even in the case of failure in one transmission line. The power plant receives the power for starting and shutting down the reactor via two Tomioka Lines as the main circuits, or via two 66 kV lines (Iwaido Line) as the backup circuit.

In the event of a blackout of these two Tomioka Lines and two Iwaido Lines, the emergency electricity to safely shut down the reactor is powered by emergency diesel generators (D/G) and D/G in the high pressure core spray system (HPCS).

The Iwaido and Tomioka lines are shared by all units. 7